Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing the claimed design.

The dash-dot-dash lines illustrate a display screen or portion thereof that form no part of the claimed design. The evenly spaced broken lines illustrate portions of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 